Directories are, by default, created with permission mode 755, but
this is not desirable for all directories. In the commands above, two
changes are made—one to the home directory of user root, and another to the directories for
temporary files.

The first mode change ensures that not just anybody can enter the
/root directory—the same as a
normal user would do with his or her home directory. The second mode
change makes sure that any user can write to the /tmp and /var/tmp
directories, but cannot remove another user's files from them. The
latter is prohibited by the so-called “sticky bit,” the highest bit (1) in the 1777 bit
mask.

6.5.1. FHS Compliance Note

The directory tree is based on the Filesystem Hierarchy Standard
(FHS) (available at http://www.pathname.com/fhs/).
In addition to the FHS, we create compatibility symlinks for the
man, doc, and info
directories since many packages still try to install their
documentation into /usr/<directory> or /usr/local/<directory> as opposed to
/usr/share/<directory> or
/usr/local/share/<directory>.
The FHS also stipulates the existence of /usr/local/games and /usr/share/games. The FHS is not precise as to
the structure of the /usr/local/share
subdirectory, so we create only the directories that are needed.
However, feel free to create these directories if you prefer to
conform more strictly to the FHS.